Đáp án+Giải thích các bước giải:
$1) x^2-6x+5=x²-1-5x+5=x(x-1)-5(x-1)=(x-1)(x-5)$
$2) x^2-8x+15=x²-3x-5x-15=x(x-3)-5(x-3)=(x-3)(x-5)$
$3) x^2+9x+36=x²+4x+9x+36=x(x+4)+9(x+4)=(x+4)(x+9)$
$4) x^2+7x+12=x²+3x+4x+12=x(x+3)+4(x+3)=(x+3)(x+4)$
$5) 4x^2-x-5=4x²+4x-5x-5=4x(x+1)-5(x+1)=(x+1)(4x-5)$
$6) x^2-x-20=x²+4x-5x-20=x(x+4)-5(x+4)=(x+4)(x-5)$
$7) x^2+4x-12=x²+2x-6x-12=x(x+2)-6(x+2)=(x+2)(x-6)$
$8) 3x^2-7x+4=3x²-3x-4x+4=3x(x-1)-4(x-1)=(x-1)(3x-4)$
$9) 2x^2-17x+9=2x²+x-18x-9=x(2x-1)-9(2x-1)=(2x-1)(x-9)$
$10) x^2-11x+6=x²+x-12x+6=x(x-1)+6(2x-1)$
$11) 4x^2+16x-9=4x²-2x+18x-9=2x(x-1)+9(x-1)=(x-1)(2x-9)$
$12) 6x^2+7x+2=6x²+3x+4x+2=3x(2x+1)+2(2x+1)=(2x+1)(3x+2)$